The fuel tank to be installed in motor vehicles wherein natural gas is used as the engine fuel is provided with a safety valve for preventing bursting due to the buildup of the internal pressure of the tank with a rise in the temperature of the tank. The publication of JP-A No. 2001-317645 discloses a safety valve of the type mentioned which comprises a main body, piston (movable body) housed in the main body, meltable alloy filled in a space inside the main body around the piston, and biasing member provided between the piston and the main body. The piston has a passageway extending from one end thereof to the other end thereof, and a first pressure receiving face and a second pressure receiving face at its opposite ends.
Safety valves of the type mentioned are used not only for natural gas tanks but also for hydrogen gas tanks for fuel cell vehicles, so that it has been desired to develop such valves which ensure improved safety.
An object of the present invention is to provide a safety valve of improved safety to be attached to a container for the escape of gas from the container in the event of a rise in temperature.